THE BASIC'OPEN-HEARTH PROCESS. 205'
remainder, together with 400 pounds of ore, was used alter melting,.but in spite of the incorporation of this basic material into the slag; during, the interval between the two stages at which the samples were taken, it will be seen that a uniform composition was maintained. .
'',.' r" ..'.. ..;;..",; ... . , TABLE Xl-L.... . : . .,,..'.. Slag Analyses of Twenty-seven Basic Open-Hearth Heats.
— '•'' '•'''•'•'' ' Slag. •':::'" •'' Composition, per cent. . •
SIOa. PS0.. CaO. FeiD.
After melting^ . . ...... .... 14.85 12,40 15.53 18.73 45.07 45.40 9.00 12,60
Before tapping ..............
/SEC. XIn.—Eecarburiwtion and rephosphorization.—Keearburj-zation, is .carried on in the same way as in acid work. A complicating condition is- added when either the stock or the ore contains, any considerable proportion of manganese, for .the decarburized metal may then hold as much as .20 or .30 per cent, of Mn. Not only must this be allowed for in the final addition, but the bath contains less oxygen under these circumstances, and there will be less loss of metallic manganese during the reaction. There is also danger of rephosphorization, or the return of phosphorus from slag -to metal. In the basic-Bessemer this is a source of considerable trouble, but in the open-hearth the recarburizer is almost always added in a solid state and the metal probably contains less oxygen, so that the reaction is less violent. Moreover, during the solution of the ferro, the slag is at work with its dephosphorizing influence, so that the sum total of the reactions may even show a decrease in phosphorus. Other things being equal, it would seem probable that a slag containing a high percentage of phosphoric acid will hold this component less firmly than a purer cinder, and I have tried to illustrate this point* by experiments, the results of which may^ be summarized as follows:
(1) With slags containing under 5 per cent. P205 and not over 20 per cent. Si02, the rephosphorization need not exceed .01 nor average over zero per cent.
(2) With slags containing from 5 to 10 per cent. P205 and not
* The Open-Hearth Process. A. I. M. JB., Vol. XXII, p. 484..